Two psalms are attributed to “Ezrahites” – the superscription to Psalm 88 says it is “A Maskil of Heman the Ezrahite” and Psalm 89 “A Maskil of Ethan the Ezrahite”. Book III of the psalter (Psalms is made up of 5 books) concludes with these two psalms.
Psalm 88, as it stands in the Masoretic Text and all the ancient versions, attributes authorship to both “the Korahites” (בני קרח is literally “sons of Korah”) and to “Heman the Ezrahite”. James Thirtle  argued that the phrase “A song, a psalm of Korahites”, should be placed at the end of Psalm 87 which is explicitly described in its superscription as “Of the Korahites; a psalm; a song”, leaving the title “a maskil of Heman the Ezrahite” in place as the title of Psalm 88. He cited Franz Delitzsch who commented that there are here “alongside of one another two different statements” as to the origin of one psalm, and asked “which notice is the more trustworthy?”  This explanation creates the difficulty that Psalm 87 would then be the only psalm to have an almost identical description in both its superscript and postscript, although this would be less of a difficulty than Psalm 88 being attributed to two different authors, and it frees Psalm 88 from its awkward association with the Korahites as it differs from the other Korahite psalms in content. 
Psalm 88 is distinguished as possibly the most negative, pessimistic psalm in the Bible! The writer complains that his life is miserable, that he is at the point of death, and, in a very Job-like way, describes his situation as being abhorent to his companions who shun him. He further complains that God has turned away from him, and blames God for his misfortunes. It ends abruptly without a glimmer of hope.
It’s not unusual for writers of Psalms to complain about their situation. In fact, “complaints” are the largest category of psalms. Typically, however, these psalms end with the writer turning to God in their misery and praising him for delivering them from their calamity. Not Psalm 88! Heman doesn’t have a positive word to say about his situation and he has apparently has no reason to praise God. So what went wrong? Why is this psalm different? My theory is that it’s an unfinished work and that the writer died before it was completed. Having described his situation as worsening, and complaining that he was at the point of death, it makes sense that he abruptly died!
Perhaps Psalm 89 was an attempt by a relative to “balance” the despair and hopelessness of Heman’s complaint with a more positive and hopeful psalm. It opens by praising God for his steadfast love and is mostly positive throughout.
 James William Thirtle, The Titles of the Psalms: their Nature and Meaning Explained. London: Henry Frowde, 1904, p13-14
 Franz Delitzsch, Commentary on Psalms (trans. Bolton; Grand Rapids: William B Eerdmans Publishing Company, reprint 1973), vol iii, 24
 Bruce K. Waltke, “Superscripts, Postcripts, or Both,” Journal of Biblical Literature 110, no. 4 (1991): 592